Hydraulic props or struts



Sept- 19, 1961 M. J. MARLow 3,000,358

HYDRAULIC PROPS OR STRUTS lNvEN-roR la/ufl. -T- MKLov/ BY y gina,

ATTORNEY:

Sept. 19, 1961` M. J. MARLow '3,000,358

HYDRAULIC PROPS OR STRUTS Filed Feb. l5, 1960 2 Sheets-Sheet 2 INVENTQQ Haw/4:1. JT NARLovV BY M Mr ATTORN EVS United States Patent Otiice Patented Sept. 19, 1961 f This invention relates to hydraulic telescopic props comprising a cylinder member and a ram member together enclosing a liquid pressure chamber into which hydraulic liquid is transferred yfor extending the prop, and from which the liquid under the hydraulic pressure caused by excessive longitudinal compression loads applied to `the prop, can escape through a relief valve.

It is an object of the invention to provide a relief valve fwhich is of robust construction and which can be adjusted to open at a predetermined compression load on the prop.

In contrast to known relief valves which incorporate some form of conventional spring preloaded against the movable member of the valve, the present invention utilizes the longitudinal strain of the ram member under the opposed forces of externally applied load and hydraulic pressure to open the relief valve.

'IIwo -forms of pit prop in accordance with the invention are illustrated in longitudinal section in FIGURES l and 2 respectively of the accompanying drawings.

FIGURE 'l shows a hydraulic prop comprising a cylinder member having a cylinder with a floor-engaging base 1f1 fixed at its lower end and a bearing ring 12 fixed at its upper end. The ram member comprises a tube 13 which slidably enters the bearing ring 12, wherein a wiper ring 14 is iitted, while its lower end carries an inner bearing ring 15 and a piston head 1'6 both slidable in the bore 17 of the cylinder 10. A high pressure packing gland `assembly 18 is seated against a shoulder 19 on the lower side of the piston '16 land is located by a retaining ring 21 which is part of a cap fixed to the piston 16. A head 22 ixed to the upper end of the ram tube 13 is surmounted by a roof-engaging cap 23 which is replaceably secured by a bolt 24. The cavity 25 within the ram tube is open to atmosphere through a hole 26 in the 'head 22 and then through the clearance in the hole 27 4in the :head 22 and cap 23 through which the bolt 24 is iixed.

The pressure chamber 28 enclosed ybetween the cylinder 10, the base 11 and the piston 16 is connected by a feed tube 29 with an inlet valve 31 which is fixed in the head 22 and contains a spring-loaded non-return ball valve 32. The inlet valve 31 is adapted for connection with an external source of hydraulic fluid under pressure from an appliance which may be readily attached or disengaged from the groove 33 in the inlet valve 31.

A cylindrical valve housing 34 is fixed centrally in the piston 16 and is provided with a central bore 35 leading to a circular valve seat 36 which is of less diameter than the lbore 35. A ball valve 37 located in a cylindrical guide member 38 which is slidable -in the bore 35 is urged upwardly against the seat 36 by a spring 39 interposed between the guide member 38 and an apertured retaining plug 41. The retaining plug 41 is secured in the retaining ring by a spring circlip 42. A channel 44 between the piston 16 and housing 34 leads to a recess 45 in the bore 35 to provide communication between the pressure chamber 28 and the surface of the ball 37 on the pressure side of the valve seat 36.

A push rod 46 extending substantially throughout the length of the ram tube 13 is effectively fixed but axially adjustable in the head 22 by means of a screw driver engaged in notch 48 in the end of rod 46, and the screw thread 47, and is secured by la lock nut 49. The lower end of the push rod 46 comprises ya portion 51 of reduced diameter which extends with clearance through the upper part of the valve housing 34, this clearance 52 opening into the cavity 25 through -a cross drilling 53 in the upper part of the valve housing 34.

When the hydraulic prop is placed between the floor and roof of a mine and injected with hydraulic fluid under pressure through the inlet valve 31, it extends from the closed position shown in FIGURE 1. As the mine roof.

settles, the hydraulic pressure in the chamber 28 will rise progressively with the externally applied load on the cap 23. It has been yfound that these opposed loads cause a small but appreciable strain of the ram tube 13 in longitudinal compression and according to this invention this strain is utilized to make the ball valve 37 operate as an excess pressure relief valve. VTov achieve this, the hydraulic prop without the cap 23 iitted -thereto is put in a testing machine which is capable of exerting the required maximum load-supporting thrust of the prop. The push rod 46 is then turned by means of the slot 48 in its upper end until the lower end lifts the ball 37 off its seat 36 at yany load in excess of the required maximum. The lock nut 49 is then tightened, the prop removed from the testing machine, and the cap 23 tted. When the prop is unloaded there will be a clearance between the push rod y46 and the -ball valve 37 and Ithis clearance will progressively reduce to zero when' the prop is subsequently :loaded in use up to the specified yield point. rod 46 is not subject to hydraulic load and the force required to lift the ball 37 off its seat 36 against the pressure in the chamber 28 is insuicient to cause any appreciable compression of the push rod 46.

FIGURE 1 does not show a valve lwhich enables the prop to be collapsed when it is withdrawn, but is intended simply to show the `operation of an excess pressure relief valve which is opened when the ram tube yields compressively Iunder liquid pressure.

FIGURE 2 -illustrates a hydraulic pit prop having a relief valve operable in similar manner but also including supplemental means whereby the relief valve can be opened under manual control to enable the pit prop to be withdrawn. In this construction the cylinder member comprises a cylinder 60 having -a floor-engaging base 61 secured to its lower end, an upper bearing ring 62 together with a wiper ring 63 secured at its upper end, and a lower bearing ring 64 secured in au intermediate position within the cylinder 60. The ram member comprises an outer tube r65 slidable within the bearings 62 and `64, a roofengaging cap 66 iixed at its upper end, a circlip 67 let into its lower end to co-operate with the lower bearing ring 64 in providing an extension limit stop,a ring 68 is secured within the lower end of the outer tube 65, and an inner tube 69 is fixed within the ring 68 co-axial with but spaced from the outer tube 65. The inner tube 69 is closed at its upper end by a head 71 to separate a liquid reservoir 72 within the outerY tube -65 from lthe interior of the inner tube `69. A pressurechamber 73 within the latter is closed lfrom below by a piston tubeY 74 which is slidable in the inner tube 69 and secured at its lower end to the licor-engaging base 61. A packing ring assembly 75 trapped between the lower end of the inner tube 69 and the ring 68 maintains a sliding seal between the inner tube 69 and piston tube 74.

A housing 76 for valve-operating mechanism is mounted transversely in the upper part of the outer tube 65. At one end of the housing 76 a non-return inlet valve 77 is provided. This inlet valve 77 is urged against a seat 78 by a spring 79 but is movable olf Vits seat by the application of air pressure from an external source to a nozzle 81, this air pressure passing into the reservoir The push 72 through an opening 82 in the housing. A blow-olf valve 83 seated against the central opening 84 in the inlet valve 77 by a spring 85 permits air to escape from the reservoir upon contraction of the prop as will be described'.n The reservoir 7|2i's partially lled with hydraulic liquid and a liquid supplyV pipe 86 opening from the lower part of the reservoir 72 is xed in the head 71 to supply hydraulic liquid under air pressure applied at the nozzle 81 toa central bore- 87 behind a valve. seat 88. A ball valve 89 lightly loadedv against the valve.v seat 88 by a spring 91 opens under pressure in the reservoir 72 to. admit hydraulic liquidl to the pressure chamber 73.

VThis ballvalve 89- is alsov arranged to operate both as an excess pressure relief Avalveand as a pressure release valve by the mechanism now to be described. This mechanism comprises a push rod 92 mounted in the bore 87' and extending upwardly to a head portion 93 which entersy the housing 76, While a compression spring 94 seated against the head Y71V of the inner tube 69 acts upwardly on the headv 93 of the` pin 92. The head 93 supports a steel ball 95 which is guided within a vertical bore 96 in the housing 76 and which projects partly into a horizontal bore 97 formed in the housing 76. Two similar steel balls. 98 and 99 are guided within the bore 97, the ball 98 cooperating with an adjustable screw stop 101 secured by a locking nut 102, and the ball 99 being disposed adjacent the stem 103 of a plunger 104. The plunger 104 is slidable in a counterbore 105 which is co-axial with and of larger diameter than the bore 97, while a spring 106 seated against the step between the bores 97 and 105 urges the plunger 104 outwardly.

A slottedy lug 107, of which one arm is seen in FIGURE 2, projects outwardly from the housing 76 and supports a pin 108 on which a release cam l109 is pivoted. The release cam also carries a pivot 110 on which a release shackle 111 is mounted.

The operation of the prop will now be described. To set the prop between the floor and roof of a mine, air pressure is applied to the nozzle 81 and enters the reservoir 72 past they inlet valve 77, forcing hydraulic liquid in the reservoir through the pipe 86 and past the ball valve 89 into the pressure chamber 73, thus extending the inner tube 69 and the outer tube 65 from the piston tube 74 and the cylinder 60. Upon removal of the pressure connection to the nozzley 81, excess air pressure in the reservoir willr escape past the blow-ofi valve 83, and the ball valve 89 will seal against the valve seat 8S. When the prop isY compressed under yielding of the mine roof the pressure in the pressure chamber 73 applies a tension load ony the inner tube 69 and, by means of the connection provided by the ring 68, a compression load on the outer tube 65. The displacement of the head 71 relative to the push rod 92 which is effectively fixed for operation of the ball valve 89 as a relief valve is therefore the summation of the compressive strain of the outer tube 65 and the tensile strain of the inner tube 69.

VIn the pit prop of FIGURE 1, the compressive strain of the ram tube 13 can be calculated from its length, net'cross-sectional area, elastic modulus and applied load.

For example, if the length-125.66 inches Y Net cross-sectional area=2.45 square inches Elastic modulus=13,000 tons per square inch Applied load-:22 tons a strain of v0.0177 inch is calculated.

Ifthereforerthe normal clearance between the push rod 46 and the ball 37 is equal to 0.0177 inch, this clearance will be reduced progressively to zero when the applied load reaches 22k tons,A so that beyond this load the push rod.46 unseats the ball 37.

In the. pit prop of FIGURE 2, the added strains of the two tubes 65 and 69 willbe substantially greater than that calculated in thepreceding example.. The ballvalve 89gwill therefore be displaced further from its seat 88 4 for a given load in excess of the predetermined maximum applied load.

I claim as my invention: 1. A hydraulic prop for the support of an externally applied load from a resisting base through pressurization of contained liquid, said propl comprising4 at least two telescopic cylinder and ram members mounted slidably-` one in the other and together enclosing a liquid' pressure chamber, one part of the ram member having a passageway connecting the inside and the outside of the pressure chamber, a valve disposed in saidV passageway, and'v a valve-operating'element eiectively fixed in another part of the ram member separated from the one part in which the valve is disposed by a portion of the ram: member whichA is subject to longitudinal strain under the opposed forces of the externally applied loady on the ram member and the resulting liquid pressure in the pressure chamber, the valve-operating element being disposed in co-operative association with the valve to open same as an excess pressure relief valve when the longitudinal strain in the ram member exceeds a predetermined value.

2. A hydraulicV prop according to claim 1, wherein the valve comprises a valve seat fixed in the said one part of the ram tube, and a movable Valve element engageable with that side of the valve seat which is subject tol liquid pressure in the pressure chamber, and wherein the valveoperating element comprises a push rod which, under said longitudinal strain in said portion of the ram member, is. movable relatively to the valve seat in a direction to displace the movable valve element off said seat.V

3. A hydraulic prop according` to claim 1, wherein the portion of the ram tube which is subject to longitudinal strainV comprises concentric tubes joined together at adjacent ends, the other ends. of the concentric tubes being joined respectively to the one andl other said parts of the ram tube, and the inner tube at least being subjectto liquidl pressure in the pressure chamber whereby it is strained longitudinally in tension while the outer tube to which it is joined is strained longitudinally in compress1on.

4. A hydraulic prop for the support of an externally applied load from a resisting base through pressurization of contained liquid, said prop comprising telescopic cylinder and ram members for engagement the onek with the load and the other with the resisting base, and mounted slidably one in the other and together enclosing a liquid pressure chamber, a valve disposed in one part of the ram member, a passageway closable by said valve and extending between the inside and the outside of the pressure chamber, a valve-operating element disposed in another part of the ram member'separated from the one part by a portion of the ram member which is'subject to longitudinal strain under the opposed forces of the externally applied load on theram member and the resulting liquid pressure in the pressure chamber, adjustable stop means fixed in said other part of the ram member, the valve-operating element being disposed in co-operative association with the adjustable stop means and with the valve to open same when the longitudinal strain in the ram member exceeds a predetermined value for which the adjustable stop means is set.

5. .A hydraulic prop according to claim 4, including manually operable valve release mechanism mounted in the ram member in operative connection with the valveoperating element to displace same from the adjustable stop means in the valve-opening direction.

6. A hydraulic prop for the support of an externally applied load from :a resisting base through pressuriza-V tion of contained liquid, said prop comprising a cylinder member having a 4base and a piston abutting at one end against the base, a ram member slidably mounted in the cylinder member, said ram member including an outer tube having a cap at the end thereof remote from the base, an inner tube secured to the oppositey end of the, outer tube and extending inv spaced relation within the.

outer tube, a head xed to the other end of the inner tube, said head, inner tube `and the piston slidably mounted therein together enclosing a pressure chamber, a passageway in the head including a valve seat therein, a Vale element closable on the valve seat under liquid pressure in the pressure chamber, and a push rod mounted in fixed location Within the outer tube adjacent the end thereof having a cap, the push rod extending into co-operative association with the valve element to lift same ott the valve seat under the combined movement of compressive strain in the outer tube and tensile strain in the inner tube caused by an excessive externally applied load on the cap and the resulting liquid pressure in the pressure chamber acting against the head of the inner tube.

7. A hydraulic prop comprising at least a cylinder and a cooperating tubular ram member closed at their pposite ends and telescopingly slidable one Within the other, one being arranged to react from a floor as a resisting base and the other to react from a roof which constitutes an applied external load to be supported from the floor, and together enclosing a liquid pressure charnber, the liquid wherein is pressurized to resist such loading, land at least one of said members being subject to strain under the influence of the opposed forces of the applied external load and the resisting internal hydraulic pressure, a passageway formed in the latter member connecting the inside and the outside of the pressure chamber, a valve normally seated in and closing said passageWay, and a valve-operating member supported in the same member, but at a location distant from the valve and where it is not itself subject to such strain, and extending into the vicinity of said valve to contact the latter when the strain exceeds a predetermined value, and thereby to unseat the valve.

8. A hydraulic prop .as in claim 7, including a piston closing the end of the inner tubular member which is distant from the otherwise closed end of the same, and dening the pressure chamber intermediate said piston and the closed end of the outer tubular member, the passageway being formed in said piston, Land the valveoperating member comprising a push rod effectively fixed at its one end in the closed end of the inner tubular member and extending almost to the valve, in position to unseat the latter when compressional strain of predetermined amount exists in said inner member.

References Cited in the tile of this patent UNITED STATES PATENTS 1,699,917 Pomeroy Jan. 22, 1929 1,899,534 Steedman IFeb. 28, 1933 2,402,265 Thompson June 18, 1946 2,621,631 Dowty Dec. 16, 1952 2,638,075 Towler May 12, 1953 

